<template>
  <ul class="list">
    <li class="item"
        v-for=" item of letters"
        :key="item"
        :ref="item"
        @click="handleLetterClick"
        @touchstart.preventnpm="handleTouchStart"
        @touchmove="handleTouchMove"
        @touchend="handleTouchEnd"
    >
         {{item}}
    </li>
  </ul>
</template>

<script>
  export default {
    name: "CityAlphabet",
    data(){
      return{
        touchStatus:false,
        startY: 0,
        timer: null
      }
    },
    updated() {
      this.startY= this.$refs['A'][0].offsetTop
    },
    props:{
      cities:Object
    },
    computed:{
      letters(){
        const letters = []
        for (let i in this.cities){
          letters.push(i)
        }
        return letters
      }
    },
    methods:{
      handleLetterClick(e){
        this.$emit('change',e.target.innerText)
      },
      handleTouchStart(){
        this.touchStatus = true
      },
      handleTouchMove(e){
        if (this.touchStatus){
          if (this.timer){
            clearTimeout(this.timer)
          }
          this.timer = setTimeout(() =>{
            const touchY = e.touches[0].clientY - 79
            const index = Math.floor((touchY-this.startY)/20)
            if (index>=0 && index < this.letters.length){
              this.$emit('change',this.letters[index])
            }
          },20)

        }
      },
      handleTouchEnd(){
        this.touchStatus = false
      }
    }
  }
</script>

<style lang="stylus" scoped>
  @import "~styles/variable.styl"
  .list
    display flex
    flex-direction column
    justify-content center
    text-align center
    top 1.58rem
    right 0
    bottom 0
    width .4rem
    position absolute
    .item
      line-height .4rem
      color $bgColor

</style>
